Compositions which are effective in removing siccative coatings from a wide variety of substrates, including wood and metals, are known. They find utility in such diverse operations as furniture stripping and similar applications which may be characterized as home restoration operations, as well as in industrial applications, such as in the automotive industry, when it becomes necessary to remove protective siccative coatings from the component metallic parts.
The simplest of the stripping compositions comprises an aqueous alkaline solution which is usually employed at high temperature (usually a rolling boil). This is a relatively slow process in which the alkaline base is consumed and contaminants are formed in the composition.
An improvement over the use of simple solutions of alkaline bases at higher temperatures has been obtained by adding to the alkaline solution a wetting agent which accelerates the stripping operation by penetrating or permeating the paint films. Additional improvements can be realized by the use of detergents and emulsifiers which further accelerate the stripping process.
Although the aforementioned aqueous alkaline compositions, which contain wetting agents, detergents and emulsifiers and are employed at elevated temperatures and are often characterized as "hot stripper compositions", are generally effective in removing most siccative finishes, they are ineffective in removing cathodic electrodeposition paints and are not particularly effective in removing certain paints such as acrylic and vinyl paints.
It has previously been found that the addition of furfuryl alcohol, tetrahydrofurfuryl alcohol, mixtures of said alcohols, and alkoxylated furfuryl alcohol to such hot stripper compositions results in compositions that are effective in removing acrylic and vinyl paints as well as cathodic electrodeposition paints.
However, problems were encountered in the use of such stripping compositions. For example, furfuryl alcohol and water form an azeotrope, the boiling point of which falls within the operative temperature range for the hot stripper compositions. Thus, with continued use, the activator, i.e. the furfuryl alcohol, is lost as it is boiled off, thus requiring either the preparation of a new bath or the continued replacement of the furfuryl alcohol and water.
An improved activator composition is described in Applicants' prior U.S. Pat. No. 4,366,002 (the '002 patent). The '002 patent describes an activator composition comprising at least two of the following three materials:
tetrahydrofurfuryl alcohol, PA0 R--O(CH.sub.2 CH.sub.2 O).sub.n H, wherein PA0 R is furfuryl, or PA0 R is tetrahydrofurfuryl, PA0 and n in each instance has a value of from about 0.5 to 10. PA0 (i) An ethoxylated compound of the formula EQU R'O(CH.sub.2 CH.sub.2 O).sub.n H PA0 wherein R' is tetrahydrofurfuryl and n is about 0.5 to about 10, preferably about 3 to 8. PA0 (ii) A mixture of the ethoxylated compound (i) above, namely EQU R'O(CH.sub.2 CH.sub.2 O).sub.n H PA0 wherein R' is tetrahydrofurfuryl and n is about 0.5 to about 10, preferably about 3 to 8, and an ethoxylated compound of the formula R"O(CH.sub.2 CH.sub.2 O).sub.n H wherein R" furfuryl and n is about 0.5 to about 10, preferably about 0.5 to about 1.5, and more preferably about 0.85 to about 1.08. PA0 (iii) N-methyl-2-pyrrolidone. PA0 (iv) N-(2-hydroxyethyl)-2-pyrrolidone. PA0 (i) N-phenyl-diethanolamine PA0 (ii) Furfurylamine PA0 (iii) Tetrahydrofurfurylamine PA0 (iv) Octadecylamine PA0 (v) Butoxypropanolamine PA0 (vi) N-amino-morpholine PA0 (ii) A mixture of R'O(CH.sub.2 CH.sub.2 O).sub.n H and R"O(CH.sub.2 CH.sub.2 O).sub.n H, and at least one of PA0 (iii) N-methyl-2-pyrrolidone, or PA0 (iv) N-(2-hydroxyethyl)-2-pyrrolidone, and PA0 (i) N-phenyldiethanolamine PA0 (ii)Furfurylamine PA0 (iii) Tetrahydrofurfurylamine
It was found that the addition of two of the three above mentioned furfuryl compounds to an aqueous alkaline stripping bath provided compositions having increased stripping effectiveness and prolonged life when used at elevated temperatures.
The '002 patent compositions contained sequestering agents, surfactant or wetting agents, and composition-stabilizing or emulsifying agents.
Examples of these improved activator compositions and their method of use are disclosed in the '002 patent, and the disclosure of the '002 patent is incorporated herein in its entirety by reference thereto.
The compositions described in the '002 patent have eliminated the azeotrope problem inherent in the use of furfuryl alcohol and are effective in the stripping of alkyd, acrylic and cathodic electrodeposited paints. However, these compositions do not retain their activity as long as desired since the activator composition degrades at the elevated temperatures at which the stripping takes place. This requires either the replenishment of the activating composition in the alkaline stripper or the discarding of the entire stripper composition and the preparation of a new batch.